SECTION III. 



DISCUSSION OF THE ANNUAL FLUCTUATION, OF THE MONTHLY AND 



ANNUAL EXTKEMES AND OF THE SECULAR YAKIATION OF 



THE ATMOSPHERIC TEMPERATURE 



TABLES OP BESTJLTING TEMPERATURES FOE BACH DAY OP THE YEAR, OP 



OBSERVED MONTHLY EXTREMES AND OP ANNUAL MEANS POE A 



SUCCESSION OP YEARS. 



The annual fluctuation of the temperature. — The annual fluctuation in the 

 temperature of the lower atmosphere is exhibited in the progression of the succes- 

 sive monthly means, for a great number of stations in the General Temperature — 

 Tables of Section I, but it may also be shown by the tabulation of the mean 

 temperature, derived from a series of years, of every day of the year. The latter 

 method, while more advantageous, is also more laborious than the first, but is 

 indispensable in inquiries respecting certain suspected irregularities in the annual 

 fluctuation. 



In the application of Bessel's periodic function to the case of the annual fluctua- 

 tion of the temperature as derived from the monthly means, corrections are required 

 for the inequality in the length of the calendar months, and for curvature or diff^er- 

 ence in the mean monthly temperature, and the temperature for the middle of the 

 month. The first correction, for unequal length, affects principally the mean 

 annual temperature, and but slightly the periodic terms in the epochs ; the second 

 correction, for curvature, affects only the amplitude of the fluctuations. These 

 corrections may be applied separately and for each month before the application of 

 the periodic function, especially in the case where the temperature for each day is 

 known. When we have to make many applications of the formula, it becomes 

 desirable to reduce this labor as far as is possible, without sacrifice of accuracy 

 There is no need for introducing these small corrections to results from short series, 

 and it suffices to state the rules for complete quadriennia, in which, consequently, 

 the mean length of February equals 28.25 days, and the year 365.24 days nearly; 

 the average or normal month comprises 30.44 days nearly. 



The mean temperature for the months of normal length may readily be computed 

 by means of the following epochs of the ending of each month — 



22 February, 1875. f 1Q9 ) 



